The present invention relates to an electronic component, and particularly to an electronic component which is a rotary switch which has an improved type of detent spring construction, so that the detent action for said rotary switch can be stronger and more positive than heretofore practicable. In another aspect, the present invention relates to such an electronic component, incorporating a casing made of resin such as synthetic resin, which has an improved sealing construction which positively prevents ingress of soldering flux, during the process of soldering said electronic component to a printed circuit board, through a space around a terminal member which is passed through said resin casing.
In the prior art, there have been proposed various types of rotary switch type electronic components, such as so called rotary DIP switches. Such rotary switch type electronic components have typically included a disk shaped rotor member which can be rotated from the outside to actuate the rotary switching action. Typically, in such a construction, when this disk shaped rotor member is rotated, irregularities formed on its surface (either on one of its end surfaces or on its circumferential surface) drive various movable contacts to and fro, so as to make or to break various electrical or electronic circuits. Also, typically, a detent action has been provided for such rotary switching action; i.e., a detent mechanism has been provided for giving a stepwise clicking feeling to the turning action of the disk shaped rotor member, and for preferentially indexing said turning action of said rotor member to particular rotary positions. A typical prior art detent mechanism, which includes a sheet spring, will now be explained with regard to FIG. 1 of the appended drawings, which is a view of a portion of the casing of the rotary switch in which said prior art sheet spring is housed, and sheet spring being shown in plan view.
Referring to FIG. 1, the reference numeral 14 denotes a portion of the casing of this prior art rotary switch, while the reference numeral 34 denotes a disk shaped rotor member which is rotatably supported within said casing portion 14. It should be noted that the diameter of the rotor member 34 is greater than the diameter of that circular portion thereof which is visible in FIG. 1; and in fact that one of the end surfaces of this rotor member 34 which faces the viewer from the point of view of FIG. 1 is formed on its radially extreme circumferential portion--which is in fact hidden in the FIG. 1 view by the sheet spring member 10 to be described shortly--with wavy irregularities not shown in the figure. At this rotor member 34 is rotated about its rotational axis which is perpendicular to the plane of the FIG. 1 drawing paper, by a mechanism not shown in the figure said rotor member 34 opens and/or closes various contacts to provide switching action.
A detent mechanism is provided for the rotatory action of this rotor member 34, comprising a sheet spring member 10 which is shown in plan view in FIG. 1, in a position fixed to a switch casing 14 of this prior art rotary switch and ready for being pressed (in the direction forward out of the drawing paper in FIG. 1) against the radially outer circumferential portion of the rotor member 34 and against the wavy irregularities formed on said rotor member outer circumferential portion. This sheet spring member 10 is formed with an approximately square external outline, with two circular openings 52 each of which is formed in one of two substantially flat portions denoted as "F", each of which substantially flat portions "F" including one of a diagonally opposing pair of corners of said square external outline. Said openings 52 fall near said diagonally opposing pair of corners, with an approximately circular internal outline which is substantially concentric with said square external outlet. Further, the three dimensional shape of said sheet spring member 10 (not particularly shown in the drawings) is as follows: the diagonally opposed pair of portions "F" including one diagonally opposed pair of corners of the sheet spring member 10 are substantially flat and are not distorted substantially out of the plane of the drawing paper, except that each of them is formed with two very slight creases denoted as 15a1 and 15a2, and 15b1 and 15b2, which serve to slightly angle the two portions which constitute the major portion of the remainder of the sheet spring member 10 as a whole in the direction towards the viewer from the point of view of FIG. 1; while each of the other diagonally opposed pair of portions, denoted as 12a and 12b and including the other diagonally opposed pair of corners of the sheet spring member 10, is formed with three obutsely angled creases denoted as 13a1, 13a2, and 13a3 for the portion 12a and as 13b1, 13b2, and 13b3 for the portion 12b. The obtuse angles of the creases 13a1 and 13b1 face away from the viewer from the point of view of FIG. 1, while on the other hand the obtuse angles of the creases 13a2, 13a3, 13b2, and 13b3 face towards the viewer from the point of view of FIG. 1. Thereby, each of these diagonally opposed portions 12a and 12b of the sheet spring member 10 is formed in a shallow V shape, with the apexes or points of these V shapes being constituted by the obtusely angled creases 13a1 and 13b1 and each being displaced forwardly from the drawing paper with respect to the remainder of its portion 12a or 12b from the point of view of FIG. 1. Now, through the openings 52 formed in the other substantially flat diagonally opposed portions "F" of the sheet spring member 10 there are passed fixing pins 16a and 16b formed as projecting towards the viewer from the point of view of FIG. 1 from the surface of the switch casing 14, and these fixing pins 16a and 16b are thermally crimped over so as to securely and fixedly attach these portions "F" of the sheet spring member 10 to this surface of the switch casing 14. In this position, when the rotary switch is assembled and the rotor member 34 is pressed from the front, from the point of view of FIG. 1, with the wavy irregularities formed on the radially extreme circumferential portion of said rotor member 34 being on the side of said rotor member 34 which is turned away from the viewer, so that as said wavy irregularities are pressed against said sheet spring member 10, the apexes 13 a1 and 13b1 of the V shapes formed in the diagonally opposed portions 12a and 12b of the sheet spring member 10 are forcibly pressed against said radially extreme circumferential portion of the rotor member 34 and against said wavy irregularities formed therein, creating some distortion of these portions 12a and 12b of the sheet spring member 10 in the direction away from the viewer from the point of view of FIG. 1, and of said sheet spring member 10 as a whole, being forced at this time. Thus, as the rotor member 34 is turned, by the indexing action of these wavy irregularities thereof against these apexes 13a1 and 13b1 of the V shapes of the diagonally opposed portions 12a and 12b of the sheet spring member 10, a stepwise clicking or detent action is provided for this rotary motion, with said apexes 13a1 and 13b1 clicking into the depressed portions of these wavy irregularities by the spring action of the sheet spring member 10, thus defining preferential rotational positions for the rotor member 34, into which said rotor member 34 tends to be retained during its rotational action.
However, this construction is subject to the following problem. Namely, the stress set up in the sheet spring member 10 by the above explained distortion of said sheet spring member 10 in the direction away from the viewer from the point of view of FIG. 1 tends to be concentrated in the substantially flat diagonally opposed portions "F" of the sheet spring member 10, which are intermediate between the V shape apexes 13a1 and 13b1 of the diagonally opposed portions sheet spring portions 12a and 12b, and accordingly, with the other constructional parameters remaining the same, as the area of these substantially flat diagonally opposed portions "F" is increased, the maximum level of the stress in said substantially flat diagonally opposed portions "F" is decreased. In other words, for a determinate maximum possible level of stress in said substantially flat diagonally opposed portions "F" (this maximum possible stress level being fixed according to the material and the thickness of the sheet spring member 10), the greater the area of the substantially flat diagonally opposed portions "F", the greater the usable spring action available from the sheet spring member 10, and accordingly the greater the detent action available from this rotary switch as a whole. And plainly it is desirable to maximize the effectiveness of this detent action. However, since the fixing pins 16a and 16b for fixing the sheet spring member 10 to the switch casing 14, in this conventional illustrated construction, pass through said substantially flat diagonally opposed portions "F", the area of said substantially flat diagonally opposed portions "F" is thereby restricted, and accordingly the usable spring action available from the sheet spring member 10 is restricted, and the detent action available from this rotary switch as a whole is restricted. At worst, this can cause improper action and improper contact setting function of this rotary switch. To avoid such a problem, the sheet spring member 10 and the rotary switch as a whole may be constructed more solidly than might be strictly required if the constructional scheme were more favorable. Such unduly solid construction is costly and creates an unduly heavy and bulky switch.
Another matter relating to the construction of an electronic component will now be discussed with regard to FIG. 2 of the appended drawings, which also relates to the prior art. FIG. 2 is a sectional view showing how in a typical conventional case, the terminals for electrical connection to the outside are led through the material of the casing of an electronic component by being insert molded thereinto. In detail, as a matter of course an electronic component which is intended for being mounted to a printed circuit board comprises one or more terminals which extend from the interior of said electronic component to the outside thereof, typically passing through a casing of said electronic component, said casing typically being formed of a resin material such as a synthetic resin material. Now, during the process of fixing such an electronic component to a printed circuit base board, it is usual that the end portions of these terminals should be soldered to electrically conductive portions of a printed circuit pattern which is impressed on said printed circuit base board, and this soldering process is typically performed with the aid of the application of a soldering flux type material. It is very desirable, in fact it is essential, that this soldering flux is not allowed to penetrate into the interior of the casing of the electronic component during the soldering process. According to the conventional art as exemplarily shown in FIG. 2, the terminal members such as 20 of the electronic component were insert molded into the body 18 of the electronic component during the manufacture of said electronic component body 18 from synthetic resin by a molding process, and accordingly inner portions such as 20a of said terminal members 20 were embedded in and were enclosed by synthetic resin in the finished product. The close adhesion of the material of the electronic component body 18 to the inner terminal portions 20a prevents the intrusive penetration of soldering flux into the interior of the casing of the electronic component during the process of soldering the terminal members 20 to a printed circuit pattern on a printed circuit base board.
However, with this type of prior art construction, the problem tends to arise that, since there is typically a large difference between the coefficient of thermal expansion of the terminal member material (typically a metal) and the coefficient of thermal expansion of the electronic component body material (typically a synthetic resin) and since inevitably these terminal members 20 and also the proximate portions to said terminal members 20 of the material of said electronic component body 18 are considerably heated up during the above described soldering process, differential expansion between these members can cause gaps to open up between them, and a possibility exists of soldering flux creeping into the interior of the electronic component body 18 through these opened up gaps. This caused problems with the reliability of such electronic components, due to problems with bad contacts and the like engendered by such soldering flux ingress.